This invention relates to electrical keyboards of the type having a plurality of manually actuatable pushbutton switches. More particularly, this invention relates to electrical pushbutton keyboards of the type having a plurality of overcenter diaphragm contacts.
With the increasing trend towards miniaturization of electronic calculators, computers, terminals and other devices, there is a corresponding increasing demand for miniaturized keyboard entry devices which are low in fabrication cost, highly reliable in operation, rugged in construction, and which provide proper operator touch or feel. Recent efforts in this area of keyboard design have been directed to pushbutton keyboard switch assemblies employing overcenter diaphragm contacts.
Keyboards are known which include a plurality of manually actuatable pushbutton members for enabling data entry into an associated electronic device, such as a calculator or a computer. As illustrated in U.S. Pat. Nos. 3,749,859 and 3,684,842, in typical keyboards of this type, each pushbutton is provided with an associated underlying movable curved diaphragm contact element, an associated fixed contact element and a common conductor plane to which each diaphragm contact element is electrically connected. Upon actuation of a given pushbutton, the movable curved contact element is deformed in such a way as to make contact with the fixed contact element, thereby closing an electrical circuit. Upon subsequent release of the pushbutton, the pushbutton is biased in the opposite direction to the normal non-actuated state by the spring-like action of the curved contact element alone or in combination with a separate bias spring.
Known keyboard designs using diaphragm contacts suffer from several disadvantages. Some keyboards, while miniaturized to a convenient size, employ a relatively large number of working parts and are thus relatively expensive to fabricate and prone to early failure. Others do not provide proper operator touch or feel. Still other keyboard designs are compatible with only a relatively small number of keyboard pushbutton patterns, are limited in the number of functional pushbuttons which can be accommodated, and are compatible with only a relatively small number of electrical switching circuit arrangements.